The candidate's long-term career goals are to further the understanding of the organization of chromosomes, the genetic control of chromosome behavior and the evolution of multigene families. These general goals are reflected in this proposal, the goals of which are to analyze the promotion of asynaptonemal X:Y pairing by rDNA and to explore the maintenance of rDNA sequence homogeneity through non-allelic recombination in Drosophila melanogaster. The proposed experiments follow from the observation, detailed in Preliminary Studies, that a single cloned, transformed rDNA cistron stimulates X:Y pairing when located on a pairing- deficient X chromosome. Variation in sequence, position and copy number of the rDNA gene will be induced by hybrid dysgenesis utilizing the location of the rDNA in a non- autonomous P transposon susceptibe to destabilization (to generate a set of overlapping deletions) and remobilization (to generate new X insertions). Variants will be analyzed molecularly and tested for expression (transcription, mini- nucleolus formation, and ribosome production), recombination, and stimulation of X:Y pairing. By comparing sequence and position requirements for each of the rDNA phenotypes, insights into the mechanisms of recombination and pairing are expected. Tests of X chromosomes with multiple rDNA inserts will assess the role of redundancy in X:Y pairing. Although predominately an undergraduate institution, UW-Eau Claire strongly encourages independent faculty research. Space for this project has been made available in a three-room, newly renovated laboratory. Necessary equipment has been purchased by a combination of federal and university funds. Student assistants are provided. The RCDA would provide badly needed release time from the rather heavy teaching load at UW-Eau Claire, permitting a period of full time commitment to the research goals outlined above.